Industrial storage tanks used to contain liquids or compressed gases are common and are vital to industry. Storage tanks may be used to temporarily or permanently store fluids at an on-site location or may be used to transport the fluids over land or sea. Numerous inventions in the structural configurations of fluid storage tanks have been made over the years. One example of a non-conventional fluid storage tank having a cube-shaped configuration and support structure is found in U.S. Pat. No. 3,944,106 to Thomas Lamb, the entire contents of the patent are incorporated herein by reference.
There has been a progressive demand for the efficient storage and long distance transportation of fluids such as liquid natural gas (LNG), particularly over seas by large ocean-going tankers or carriers. In an effort to transport fluid such as LNG more economically, the holding or storage capacity of such LNG carriers has increased significantly from about 26,000 cubic meters in 1965 to over 200,000 cubic meters in 2005. Naturally, the length, beam and draft of these super carriers have also increased to accommodate the larger cargo capacity. The ability to further increase the size of these super carriers, however, has practical limits in the manufacture and use.
Difficulties have been experienced in the storage and transportation of fluids, particularly in a liquid form, through transportation by ocean carriers. A trend for large LNG carriers has been to use large side-to-side membrane-type tanks and insulation box supported-type tanks. As the volume of the tank transported fluid increases, the hydrostatic and dynamic loads on the tank containment walls increase significantly. These membrane and insulation type of tanks suffer from disadvantages of managing the “sloshing” movement of the liquid in the tank due to the natural movement of the carrier through the sea. As a result, the effective holding capacity of these types of tanks has been limited to either over 80% full or less than 10% full to avoid damage to the tank lining and insulation. The disadvantages and limitations of these tanks are expected to increase as the size of carriers increase.
The prior U.S. Pat. No. 3,944,106 tank was evaluated for containment of LNG in large capacities, for example, in large LNG ocean carriers against a similar sized geometric cube tank. It was determined that the '106 tank was more rigid using one third the wall thickness of the geometric cube. The '106 tank further significantly reduced the velocity of the fluid, reduced the energy transmitted to the tank and reduced the forces transmitted by the fluid to the tank causing substantially less deformation of the tank compared to the geometric cubic tank.
It was further determined, however, that the '106 configured tank did not prove suitable to handle large capacities of LNG in a large LNG carrier environment.
A further need has developed for the efficient storage and transportation of compressed natural gas (CNG) over land and sea. This includes carriers as well as Floating Oil/CNG Processing and Storage Offshore Platforms (FOCNGPSO) and floating CNG Processing and Storage Offshore Platforms (FCNGPSO). Several systems have been developed including the EnerSea Transport LLC's VOTRANS (a trademark of EnerSea) system which includes thousands of vertical or horizontal pipes which are individually filled with CNG and arranged in modules, for example on an ocean tanker. Another example is a system by SEA NG Company which involves miles of continuous piping oriented in a horizontal coil or reel called a COSELLE (a trademark of SEA NG). These self-contained coselles can be stacked vertically on one another and positioned in a tanker storage hold.
These CNG systems suffer from several disadvantages in managing the high pressure that CNG is typically stored at which can range from 2000-4000 pounds per square inch (psi) and at temperatures between around 0 and minus 30 degrees Centigrade (−30° C.). Some of these disadvantages of prior CNG storage systems include complexity in the storage tanks or systems themselves as well as significant requirements in the carrying vessel's length, beam, tonnage, propulsion, fuel consumption and the number of storage tank manifolds needed to maintain the desired temperature and pressure of the stored CNG.
Therefore, it would be advantageous to design and fabricate storage tanks for the efficient storage and transportation of large quantities of fluids such as LNG or CNG across land or sea. It is further desirable to provide a storage tank that is capable of being fabricated in ship yards for large tankers that further minimizes the number of components and minimizes the different gages or thickness of materials that are needed for the tank. It is further advantageous to provide a modular-type tank design which facilitates design, fabrication and use in the field.